Cryotron type switching device



July 23, 1963 Q P. H. KECK 3,098,967

CRYOTRON TYPE SWITCHING DEVICE Filed Jan. 9, 1959 INVENTOR PAUL H. KFCK L L,

ATTORNE United States Patent 3,098,967 CRYOTRON TYPE SWKTCHENG DEVICE Paul H. Keck, Bay side, N33! assignor, by mesne assignments to Sylvania Electric Products line Wilmington, Dcl., a corporation ot Delaware Filed tan. 9, 1959, Ser. No. 2 85,9 63 4 main: (Cl. 323%) My invention relates to switching devices.

In one type of switching device, known to the art as a cryoton, a single layer control winding is wound about a length of wire, the wire and winding being separated from each other. The wire and the winding are both maintained at an extremely low temperature, as for example, 4 Kelvin.

The wire is formed from a metal or alloy which, in the absence of a magnetic field, is a superconductor (i.e. exhibits zero electrical resistance) at the designated temperature. Further, the wire becomes a normal electrical conductor (i.e. exhibits finite electn'cal resistance), when subjected to a magnetic field having an intensity which exceeds a predetermined minimum value.

The control winding is formed from a metal or alloy which is a superconductor at the designated temperature and which remains superconducting at magnetic field intensities substantially in excess of the minimum value previously described.

A control current fiows through the control winding and establishes a magnetic field about the wire. A load current is supplied to the wire. When the magnetic field intensity established by the control current is below the minimum value, the load current flows through the wire without attenuation. When the magnetic field intensity equals or exceeds the minimum value, the wire is triggered from its superconductive state to its normal state, and the load current is sharply reduced and can be essentially zero. In other words, the wire acts as a gate which opens or closes as the control current is suitably increased or decreased.

This device, however, has an inherently low switching speed. More particularly, the time constant of the device, which establishes the minimum time for the wire to be triggered from one state to the other, is equal to the ratio L/R, where L is the inductance of the winding and R is the normal resistance of the wire. Since the inductance is relatively high, the time constant is also relatively high, for example, of the order of a millisecond.

It is an object of my invention to provide a new and improved device of the character indicated in which the switching speeds can be sharply increased. over that hitherto obtainable.

Another object is to provide a new and improved device of the character indicated which has an extremely low inductance.

Still another object is to increase the switching speed of a device of the character indicated by sharply reducing its inductance.

In accordance with the principles of my invention, I provide a hollow cylinder and a length of wire extending axially within the cylinder. The wire and the cylinder are maintained at an extremely low temperature.

The cylinder is formed from a metal or alloy which, in the absence of a magnetic field, is a superconductor and which, in the presence of a magnetic field having an intensity which exceeds a predetermined minimum value, becomes a normal electrical conductor having a finite resistance.

A control current flows through the wire and establishes a magnetic field within the cylinder. A load current is supplied to the cylinder. When the control current falls below a critical minimum value, the resultant magnetic Patented July 23, 1963 field intensity is insufiicient to destroy the superconductivity of the cylinder, and the cylinder presents a zero resistance to the flow of the load current. When the control current equals or exceeds this minimum value, the resultant magnetic field intensity is high enough to destroy the superconductivity of the cylinder, and the cylinder presents a relatively high electrical impedance to the flow of the load current. The inductance of the wire is much smaller (for example, by several orders of magnitude) than that of the control winding hitherto employed in the art. Consequently, the minimum switching time is much more rapid than that previously obtainable, and indeed switching times of the order of microseconds are obtainable.

Illustrative embodiments of my invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 illustrates one switching device in accordance with my invention;

FIG. 2 illustrates a modification of the device of FIG. 1 as utilized for information storage;

FIG. 3 shows an alternative form of the device of FIG. 2; and

H63. 4a and 4b illustrate an alternative form of the device of FIG. 1.

Referring now to FIG. 1, a chamber maintained at the temperature of liquid helium, i.e. about 4 Kelvin (not shown), contains a hollow cylinder 19' formed, for example, from tantalum. (While cylinder 10 is shown as a completely closed cylinder, it can also be a portion of a cylinder, for example, wherein the cross section of the cylinder defines a 270 are.) A load current 1;; flows through the cylinder. A wire 12- extends axially within cylinder .ltl. A control current 10 flows through the wire and produces a magnetic field intercepted by cylinder it). When lc falls below a predetermined critical value (which depends upon the materials and dimensions of the cylinder and wire, and also upon the operating temperature), cylinder lit is superconductive and presents zero resistance to the load current flow. When Is equals or exceeds its critical value, cylinder id is triggered into its normal electrical state and presents a high resistance to the flow of the load current.

Wire 12. need not be superconductive and can therefore be made of any electrically conductive metal or alloy. However, wire 12 is preferably formed from a material, such as niobium or lead, which remains superconductive at all magnetic field intensities utilized in the particular device; under these conditions there is no appreciable power loss, since the control current can be maintained without back voltage. Further, the resistance of the cylinder (in its normal state) can be adjusted to relatively high values by using an extremely thin walled cylinder. The inductance of wire 12 is extremely low. Consequently, the resultant minimum switching speed is extremely high and can be, for example, on the order of a microsecond.

As shown in FIG. 2, the device can be converted into a storage device with the addition of a sensing element, in this example, sensing conductor 14. When cylinder it} is superconductive, the magnetic field estab lished by the control current cannot penetrate the cylinder. Consequently, conductor 14 is shielded from this field and no sensing current can be induced in conductor 14. On the other hand, when the cylinder 10 is triggered into a state of normal conductivity, the magnetic field passes through the cylinder and induces a finite sensing current in the sensing conductor 14. Hence, conductor 14 serves as a bistable element and can be used for information storage. (Conductor 14 need not be superconductive. However, to reduce losses, conaccuser Z3 ductor 14 is preferably conductive and formed from the same material as wire 12.)

As shown in FIG. 3, the sensing conductor 14 can have the shape of a sensing cylinder 16 concentrically disposed about the outside of cylinder 10. The devices of FIG. 2 and HG. 3 are otherwise identical.

The device of FIG. 1 can be manufactured in a somewhat different form as shown in FIGS. 40: and 4b. A tantalum layer 2 is applied by vacuum coating techniques on one surface of an insulating base plate 1. An insulating layer 3 is applied over a portion of the tantalum layer 2. A niobium layer 4 is applied over a portion of the insulating layer 3. A second insulating layer 15 is applied over and around the niobium layer 4 to insulatedly separate the niobium layer 4 from the tantalum layer 2. A second tantalum layer 6 is applied over and around the niobium layer 4 to insulatedly separate the niobium layer 4 from the tantalum layer 2. A second tantalum layer 6 is applied over and around the insulating layer 4 to form a cylinder with tantalum layer 2. The net result is that the two tantalum layers constitute a cylinder which functions as cylinder 10 of FIG. 1; the niobium layer 4 functions as Wire 12 in FIG. 1.

It will be apparent that additional insulating and conducting layers can be applied in sequence over the device of FIGS. 4a and 4b to provide a device of the type shown in FIGS. 2 and 3.

What is claimed is:

1. A switching device consisting of an electrically conductive cylinder, an electrically conductive wire extending axially within said cylinder, and means to maintain said wire and said cylinder at an extremely low temperature, said cylinder when maintained at said temperature being superconductive in the presence of a magnetic field having an intensity which falls below a designated minimum value and being normally conductive in the presence of a magnetic field having an intensity which is at least equal to said minimum value, and an electrically conductive sensing element extending in the same direction as said Wire, said element being positioned adjacent the outer surface of said cylinder and spaced apart therefrom.

2. A device as set forth in claim 1 wherein said element is a wire.

3. A device as set forth in claim 1 wherein said element is another cylinder concentrically disposed about the original cylinder.

4. A switching device consisting of an electrically conductive cylinder through which a load current flows; an electrically conductive wire extending axially within said cylinder, a control current flowing through said wire; and means to maintain said cylinder and said wire at an extremely low temperature at which said cylinder is a superconductor for control current values falling below a designated minimum value, said cylinder being normally conductive when said control current attains a value at least equal to said minimum value, and an electrically conductive sensing element extending in the same direction as said wire and positioned adjacent the outer surface of said cylinder, said element being magnetically shielded from said wire when said cylinder is superconductive whereby no current is induced in said element, a sensing current being induced in said element when said cylinder is normally conductive.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,884 Ericsson et al Jan. 19, 1954 2,832,897 Buck Apr. 29, 1958 2,914,735 Young Nov. 24, 1959 2,930,908 McKeon et al Mar. 29, 1960 2,944,211 Richards July 5, 1960 2,946,030 Slade July 19, 1960 3,007,057 Brenncmann et al Oct. 31, 1961 

4. A SWITCHING DEVICE CONSISTING OF AN ELECTRICALLY CONDUCTIVE CYLINDER THROUGH WHICH A LOAD CURRENT FLOWS; AN ELECTRICALLY CONDUCTIVE WIRE EXTENDING AXIALLY WITHIN SAID CYLINDER, A CONTROL CURRENT FLOWING THROUGH SAID WIRE; AND MEANS TO MAINTAIN SAID CYLINDER AND SAID WIRE AT AN EXTREMELY LOW TEMPERATURE AT WHICH SAID CYLINDER IS A SUPERCONDUCTOR FOR CONTROL CURRENT VALUES FALLING BELOW A DESIGNATED MINIMUM VALUE, SAID CYLINDER BEING NORMALLY CONDUCTIVE WHEN SAID CONTROL CURRENT ATTAINS A VALUE 